Proposed changes to mitigate condensation in wall cavities and roof spaces for NCC 2019

Water condensation on a window

The proposed changes to mitigate condensation in wall cavities and roof spaces for NCC 2019 are now available for public review and comment, through the NCC 2019 Public Comment Draft released on 8 February 2018.

What’s it all about?

Condensation in the form of mould often grows where condensation forms within the built environment. The principle physical drivers are: air pressure, temperature and humidity. These same physical conditions can occur within all built structures, in all climate types within the building (its internal environment), within its intermediate zones (subfloor and roof space zones) and within the building structure (floor, walls, ceilings and roofing materials). This natural process cannot be stopped from occurring where these conditions exist. However, buildings can be designed, constructed and used in a way that manages vapour pressure, condensation risk and subsequent mould growth.

Put simply, houses are being built to be more airtight and occupants appear to be ventilating less which leads to an increase in water laden air condensing within homes. Condensation and mould have become an accepted part of the built environment in bathrooms, wet areas and other habitable rooms within many homes and not been seen as a destructive and harmful problem by home owners, but an accepted part of the domestic setting. In its hidden form it is also a problem within interstitial spaces, sub-floor zones and roof spaces. However, in light of current international literature the conditions within these buildings, if not addressed, may impact long term and significant structural degradation, immunology and allergy health concerns for the occupants.

Anecdotal evidence is abundant and research undertaken by the ABCB supports the view that there is a large and increasing interest in the problem. Changes are being proposed for NCC 2019 to reduce the overall risk associated with condensation in residential buildings leading to damage and impacting the health of building occupants, and more specifically to reduce condensation in wall cavities and roof spaces.

Are there any implications for NCC 2019?

The NCC 2019 proposes a number of changes involving the dedicated creation of new Parts in Volume One and Two for Condensation Management. These new provisions are located in Part F6 of Volume One and in Volume Two and contain new Performance Requirements, Deemed-to-Satisfy Provisions and a Verification Method in Volume One. Specifically, the proposed Deemed-to-Satisfy Provisions contain requirements for water control membranes, permeable membranes, the ventilation of roof spaces and the discharge of exhaust systems from kitchens, bathrooms, toilets or laundries. The provisions will apply to Class 1, 2 and Class 4 parts of a building. 

How can I provide comments?

The consultation period closed Friday, 13 April 2018. Thank you for your feedback.

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